Anodizing

Anodizing is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts.

Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than does bare metal. Anodic films can also be used for some cosmetic effects with thinner transparent coatings or thicker porous coatings that can absorb dyes.

The anodizing process changes the microscopic texture of the surface and changes the crystal structure of the metal near the surface. Thick coatings are porous, so a sealing process is often needed to achieve corrosion resistance.

Anodized aluminum surfaces, for example, are harder than aluminum, but can have good wear resistance that can be improved with increasing thickness or by applying suitable sealing substances. Anodic films are generally much stronger and more adherent than most types of paint and metal plating, but also more brittle. This makes them less likely to crack and peel from aging and wear, but more susceptible to cracking from thermal stress.